Situated along the border of the Philippine and Pacific tectonic plates south of the Izu peninsula of Honshu (Japan), the volcanic Izu Islands make up the northernmost archipelago of the so-called Izu-Ogasawara-Mariana Arc (see also EBAs 147 and 189, and Secondary Area s091). The Izu Islands EBA includes Oshima (which has the highest point at 854 m) in the north and Torishima in the south, and all islands between. Native vegetation of the islands is subtropical rain forest.

The distribution patterns of the EBA's restricted-range species vary slightly, with Columba janthina breeding on all the islands from Oshima to Torishima, and Turdus celaenops and Phylloscopus ijimae on Oshima to Aogashima only.

The two species which are endemic to this EBA, namely Turdus celaenops and Phylloscopus ijimae, have recently been recorded breeding in the northern Nansei Shoto (EBA 148) c.1,000 km away (Kawaji et al. 1989, Higuchi and Kawaji 1989), but because these records are so distant from the species' core ranges in the Izu Islands, and because the numbers of birds involved are very small, the Izu Islands have been treated as an EBA in their own right.

Gorsachius goisagi used to breed commonly on Miyake and Mikura, but no nests have been located since the early 1970s, although recent sightings at Miyake suggest the possibility that the species may still breed in a relatively inaccessible forested area high on the northern slope of that island (J. T. Moyer in litt. 1996). Yellow Bunting Emberiza sulphurata, a threatened restricted-range species from central Honshu (Secondary Area s090), has also been recorded on the Izu Islands (on Miyake and Mikura) in winter (Brazil 1991).

Although both of the EBA's endemic species remain locally abundant, there are a number of threats which have caused declines. For example, on Miyake much of the forest has been replaced with the fast-growing softwood Cryptomeria japonica for timber, and on Oshima much of the natural forest has been destroyed (Brazil 1991). This removal of valuable breeding habitat, and threats acting in the wintering areas of Phylloscopus ijimae, notably deforestation in Luzon in the Philippines (EBA 151), will continue to have an effect.

An additional threat on Miyake, to which has been attributed the rapid decline of Turdus celaenops on that island, is predation by weasels Mustela sibirica, which were introduced in the early 1970s and again in 1982 to control rats (Takagi and Higuchi 1992, Moyer 1993). However, predation by Jungle Crows Corvus macrorhynchos-which have increased immensely owing to the availability of food from raw garbage-may be a more significant factor. A survey in 1992 found that all of a sample of 22 T. celaenops nests failed: 19 were destroyed by crows, one by weasels, one by domestic cats and one by an unknown predator. It is likely that the decline of Gorsachius goisagi is also attributable to predation by weasels (J. T. Moyer in litt. 1996).

As well as being important for restricted-range species, the Izu Islands are particularly notable for seabirds. For example, Short-tailed Albatross Diomedea albatrus (classified as Endangered) once bred in huge numbers on islands in the Izu-Ogasawara chain, but exploitation for feathers from the late nineteenth century onwards almost wiped out most populations by 1930, and today it only breeds on a few islands, the most important of which is Torishima in this EBA. Its breeding success has been improved there owing to grass transplantation to stabilize the nesting areas, but the population (c.500 birds) remains susceptible to volcanic eruptions (Hasegawa 1984, 1991).

Another seabird with significant breeding colonies in this EBA is Japanese Murrelet Synthliboramphus wumizusume (classified as Vulnerable) which breeds on small islands and stacks in southern Japan and South Korea. The recent increase in popularity of sport-fishing is a particular worry for this species as fishermen discard unwanted fish on isolated reefs, attracting crows and Black-tailed Gulls Larus crassirostris. During periods of bad weather when the reefs are inaccessible (and no sport-fishing takes place) these birds eat the eggs and nestlings of S. wumizusume instead (J. T. Moyer in litt. 1996).

The national government has designated the entire Izu archipelago a 'protected area', and several valuable places have been designated as 'special protected areas'. However, there are no rangers to enforce the protection, and destruction and alteration of habitat continue.

Recommended citation
BirdLife International (2024) Endemic Bird Area factsheet: Izu Islands. Downloaded from https://datazone.birdlife.org/eba/factsheet/149 on 22/11/2024.